The invention relates to improvements in continuously variable transmissions, e.g., so-called CVT transmissions which are frequently employed in the power trains of motor vehicles, and more particularly to improvements in adjustable pulleys or sheaves which are utilized in such transmissions.
Transmissions of the above outlined character comprise adjustable pulleys wherein a first flange is movable axially toward and away from a fixed second flange by a hydraulic control system which employs one or more plenum chambers and a system of valves serving to regulate the flow of oil or another hydraulic fluid into and from the chamber(s). It is also known to counteract the adverse influence of centrifugal force upon the circulating body or bodies of hydraulic fluid in the plenum chamber(s) by resorting to an additional or extra plenum chamber and by providing a path for controlled gradual outflow of fluid from the additional chamber. Reference may be had, for example, to published German patent application Serial No. 195 44 644 A1.
A drawback of presently known adjustable pulleys wherein the hydrulic adjusting or control system employs an additional plenum chamber and means for permitting gradual evacuation or expulsion of pressurized fluid from the additional chamber is that the fluid which is confined in the additional chamber opposes or prevents rapid shifting of the transmission between overdrive and underdrive or permits such shifting only if the hydraulic system which initiates and effects axial movements of the adjustable flange operates with a hydraulic fluid that is maintained at an extremely high pressure.
An object of the present invention is to provide a novel and improved adjustable pulley of the type wherein one of two coaxial flanges is movable axially toward and away from the other flange.
Another object of the invention is to provide a continuously variable transmission which employs one or more improved adjustable pulleys.
A further object of the invention is to provide a novel and improved hydraulic adjusting or control system for use in conjunction with the above outlined improved adjustable pulley.
An additional object of the instant invention is to provide a pulley wherein a first flange (such as a conical flange) is movable relative to a second flange at a desired speed and to any one of a number of different positions without being influenced by the rotational speed (and hence by centrifugal force acting upon the body or bodies of circulating fluid in the control system) of the pulley.
Still another object of the invention is to provide a novel and improved valve for use in the hydraulic control system of an adjustable pulley.
A further object of the invention is to provide a pulley which can be utilized with advantage in a transmission serving to drive the differential in the power train of a motor vehicle.
Another object of the invention is to provide a method of eliminating or reducing the influence of centrifugal force upon the circulating body or bodies of fluid in the hydraulic control system for an adjustable pulley.
An additional object of the invention is to provide a pulley which can be utilized with advantage as a superior substitute for heretofore known adjustable pulleys in continuously variable transmissions.
One feature of the present invention resides in the provision of an adjustable pulley or sheave which comprises a shaft rotatable about a predetermined axis at a plurality of different speeds, a first flange which shares all rotary movements of and can be of one piece with the shaft, a second flange which is rotatable with and movable axially of the shaft toward and away from the first flange, and fluid-operated means for moving the second flange toward and away from the first flange. Such moving means includes at least one first chamber which is arranged to receive a hydraulic fluid to thus generate a first force tending to move the second flange toward the first flange, and an additional chamber which serves to receive and confine hydraulic fluid at a plurality of different pressures to thus generate a variable second force tending to move the second flange away from the first flange. The improved adjustable pulley further comprises a valve which is rotatable with the shaft and serves to regulate the outflow of hydraulic fluid from the second chamber in dependency upon the rotational speed of he shaft.
The additional chamber can be provided with at least one outlet for the flow of hydraulic fluid, and the valve can include at least one mobile valving element which serves to regulate the outflow of hydraulic fluid from the additional chamber by way of the at least one outlet. Such valve can further comprise a valve body or housing for the at least one mobile valving element, and such valve body is connected for rotation (e.g., of one piece) with the shaft, with the first flange or with the second flange. The at least one outlet is provided in the valve body.
The mode of operation of the valve (which can be said to constitute a relief valve) can be such that the at least one valving element is movable, under the action of centrifugal force, to a first position in which it seals the at least one outlet, and to at least one second positionxe2x80x94in which the at least one outlet is openxe2x80x94when the second force increases to a predetermined value (e.g., in response to an increase in the pressure of fluid filling the at least one first chamber). The second force varies or can vary as a function of variations of fluid pressure in the additional chamber.
The valve body is or can be provided with a seat for the a least one valving element, and such valving element is being acted upon by centrifugal force when the shaft rotates so that the valving element bears upon the seat with a force which increases in response to increasing centrifugal force. The at least one outlet can include a channel which is provided in the valve body and is inclined relative to the common axis of the flanges. The magnitude of the third force can exceed the magnitude of the second force by a value which is at least substantially independent of the magnitude of centrifugal force acting upon the body of fluid in the additional chamber and being opposed by the at least one valving element.
The at least one valving element can constitute a sphere, particularly a sphere having a substantial mass.
The inlet or inlets for admission of hydraulic fluid into the additional chamber can be in communication with that portion of the additional chamber which is nearest to the common axis of the flanges.
The at least one first chamber and/or the additional chamber can be defined by a first wall which is affixed to or forms part of the shaft, and by a second wall which is affixed to the second (axially movable) flange. One of these walls is disposed between the at least one first chamber and the additional chamber.
Another feature of the present invention resides in the provision of a continuously variable transmission which comprises a first adjustable pulley that is rotatable about a first axis, and a second adjustable pulley which is rotatable about a second axis by way of an endless flexible element (e.g., a link chain) which is strained over the pulleys. The second pulley comprises a shaft which is rotatable about the second axis, a first flange which is rotatable with the shaft, a second flange which is rotatable with and is movable axially of the shaft toward and away from the first flange, and fluid-operated operated means for moving the second flange toward and away from the first flange. The moving means includes at least one first chamber which serves to receive a hydraulic fluid to thus generate a first force tending to move the second flange toward the first flange, and an additional chamber which serves to receive and confine hydraulic fluid at a plurality of different pressures to thus generate a variable second force tending to move the second flange away from the first flange. The second pulley further comprises a valve which is rotatable with the shaft and is spaced apart from the second axis and serves to regulate the outflow of hydraulic fluid from it the second chamber in dependency upon the rotational speed of the shaft.
In accordance with a presently preferred embodiment, the valve comprises a valve body which shares rotary movements of the shaft about the second axis and has a channel which is inclined relative to the second axis and is provided with a seat, and a valving element which is movable in the channel against the seat under the action of centrifugal force which develops in response to rotation of the shaft about the second axis so that the force with which the valving element bears upon the seat to prevent the outflow of fluid from the additional chamber by way of the channel increases in response to increasing rotational speed of the shaft about the second axis.
The force (SK) with which the valving element bears upon the seat under the action of centrifugal force can be determined in accordance with the equation
SK=Fxc3x97sin xcex1
wherein F is the centrifugal force acting upon the valving element and a is the extent of inclination of the channel relative to the second axis.
The first and additional chambers can receive hydralic fluid from a pump and discharge hydraulic fluid into a reservoir by way of channels, bores and ports provided in the shaft of the second adjustable pulley. Such shaft can transmit torque which serves to drive the wheels of a motor vehicle.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved adjustable pulley itself, however, both as to its construction and the mode of installing and utilizing the same in a continuously variable transmission, together with numerous additional important and advantageous features and attributes thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawings.